Aerodynamic force prediction of the laminar to turbulent flow transition around the front bumper of the vehicle using Dynamic-slip wall model LES

Gorlé²

2022

Front. Built Environ.

Natural ventilation can contribute to a sustainable and healthy built environment, but the flow can be highly dependent on the ventilation configuration and the outdoor turbulent wind conditions. As a result, quantifying natural ventilation flow rates can be a challenging task. Wind tunnel experiments offer one approach for studying natural ventilation, but measurements are often restricted to a few points or planes in the building, and the data can have limitations due to the intrusive nature of measurement techniques or due to challenges with optical access. Large-eddy simulations (LES) can offer an effective alternative for analyzing natural ventilation flow, since they can provide a precise prediction of turbulent flow at any point in the computational domain and enable accurate estimates of different ventilation measures. The objective of this study is to use a validated LES set-up to investigate the effect of the opening size, opening location and wind direction on the ventilation flow through an isolated building. The effects are quantified in terms of time-averaged and instantaneous ventilation flow rates, age of air, and ventilation efficiency. The LES results indicate that, for this isolated building case, the effect of the wind direction is more pronounced than the effect of the size and position of the ventilation openings. Importantly, when ventilation is primarily driven by turbulent fluctuations, e.g. for the 90° wind direction, an accurate estimation of the ventilation rate requires knowledge of the instantaneous velocity field.

Section: Governing Equations and Discretization Methodsmentioning

confidence: 99%

Large-Eddy Simulations of Wind-Driven Cross Ventilation, Part 2: Comparison of Ventilation Performance Under Different Ventilation Configurations

Gorlé²

2022

Front. Built Environ.

“…More details on the derivation of the Helmholtz system and the low mach equation of state (Eq. 3) may be found in Ambo et al (2020).…”

Section: Governing Equationsmentioning

confidence: 96%

Large-Eddy Simulations of Wind-Driven Cross Ventilation, Part1: Validation and Sensitivity Study

Gorlé

2022

Front. Built Environ.

Natural ventilation is gaining popularity in response to an increasing demand for a sustainable and healthy built environment, but the design of a naturally ventilated building can be challenging due to the inherent variability in the operating conditions that determine the natural ventilation flow. Large-eddy simulations (LES) have significant potential as an analysis method for natural ventilation flow, since they can provide an accurate prediction of turbulent flow at any location in the computational domain. However, the simulations can be computationally expensive, and few validation and sensitivity studies with respect to simulation parameters such as grid resolution and boundary conditions have been reported. The objectives of this study are to validate LES of wind-driven cross-ventilation and to quantify the sensitivity of the solution to the grid resolution and the inflow boundary conditions. We perform LES for an isolated building with two openings, using three different grid resolutions and two different inflow conditions with varying turbulence intensities. Predictions of the ventilation rate are compared to a reference wind-tunnel experiment available from literature, and we also quantify the age of air and ventilation efficiency. For the cross-ventilation case modeled in this paper, the prediction of the mean ventilation flow rate is very robust, showing negligible sensitivity to the grid resolution or the inflow characteristics with the maximum error of 1.9 and 1.3% for each sensitivity study. However, a sufficiently fine grid resolution is required to obtain accurate predictions of the detailed flow pattern and the age of air as they show comparably larger errors of 10 and 20% in the grid sensitivity study, and the standard deviation of the instantaneous ventilation rate is affected by the turbulence in the inflow condition with showing 44% difference.

“…This approach results in a Helmholtz equation for the density Flow E10-5 with less numerical stiffness than the Poisson system for the pressure that is typical of fully incompressible formulations. Details on the derivation of the Helmholtz system may be found in Ambo et al (2020). The governing equations for the filtered ( • ) field quantities are given by…”

Section: Governing Equationsmentioning

confidence: 99%

Large-eddy simulations to define building-specific similarity relationships for natural ventilation flow rates

Gorlé

2023

Flow

Natural ventilation can play an important role towards preventing the spread of airborne infections in indoor environments. However, quantifying natural ventilation flow rates is a challenging task due to significant variability in the boundary conditions that drive the flow. In the current study, we propose and validate an efficient strategy for using computational fluid dynamics to assess natural ventilation flow rates under variable conditions, considering the test case of a single-room home in a dense urban slum. The method characterizes the dimensionless ventilation rate as a function of the dimensionless ventilation Richardson number and the wind direction. First, the high-fidelity large-eddy simulation (LES) predictions are validated against full-scale ventilation rate measurements. Next, simulations with identical Richardson numbers, but varying dimensional wind speeds and temperatures, are compared to verify the proposed similarity relationship. Last, the functional form of the similarity relationship is determined based on 32 LES. Validation of the surrogate model against full-scale measurements demonstrates that the proposed strategy can efficiently inform accurate building-specific similarity relationships for natural ventilation flow rates in complex urban environments.